1. Field of the Invention
The present invention relates to a machine tool driving control apparatus for rotating a workpiece about a predetermined axis, and moving at least one of the workpiece and a tool for machining the workpiece, thereby machining the workpiece into a desired shape.
2. Related Background Art
In general, a machine tool driving control apparatus of this type has a controller for controlling driving of a spindle rotating motor for rotating a spindle capable of holding a workpiece, a tool moving motor, a workpiece moving motor, and the like. When a workpiece (spindle) is to be rotated and machined (e.g., cut), the controller controls driving of the spindle rotating motor so as to set the rotational speed of the workpiece (spindle) during machining the workpiece in order to keep machining conditions as constant as possible. For example, when the diameter of a machined (cut) portion of a workpiece rotated at a constant speed gradually increases, the peripheral speed of the workpiece also increases. Assuming that the moving speed of the tool is constant, the relative moving speed between the workpiece and the tool increases to change the machining (cutting) speed by the tool. Therefore, when the diameter of a workpiece at a machined (cut) position changes, the rotational speed of the workpiece (spindle) is changed in accordance with the change in diameter so as to machine the workpiece under the same conditions.
As described above, when the rotational speed of a workpiece (spindle) is changed to a predetermined one during machining, or a workpiece (spindle) is to be rotated at a desired rotational speed in order to start machining, a long time is taken before variations in the rotational speed of the workpiece (spindle) settle, and the rotational speed of the workpiece (spindle) converges to a predetermined one. The controller controls the tool moving motor and workpiece moving motor so as to stand by without any machining operation until the rotational speed of the workpiece (spindle) stabilizes to a predetermined one. For example, the controller determines upon the lapse of a predetermined time that variations in rotational speed settle, and controls to start machining by the tool. The controller detects the rotational speed of a workpiece (spindle), and when the detected rotational speed falls within a predetermined threshold range, controls to start machining by the tool.
However, if machining operation stands by until the rotational speed of a workpiece (spindle) converges to a predetermined one, as described above, a time until the tool moving motor and workpiece moving motor are driven to actually machine the workpiece by the tool is wasteful. This prolongs the machining time to decrease the productivity. Even if a standby time till the start of machining, or the threshold of a machining start rotational speed is strictly determined by experiment or the like, it is limited to shorten a time until the tool actually machines a workpiece. In this manner, a conventional machine tool driving control apparatus cannot increase the productivity.
The present invention has been made in consideration of the above situation, and has as its object to provide a machine tool driving control apparatus capable of rapidly, efficiently machining a workpiece, and increasing the productivity without decreasing the machining accuracy of the workpiece by a tool.
According to the present invention, a machine tool driving control apparatus for rotating a workpiece about a predetermined axis, and moving at least one of the workpiece and a tool for machining the workpiece, thereby machining the workpiece into a desired shape is characterized by comprising workpiece rotational speed changing means for changing a rotational speed of the workpiece about the predetermined axis into a predetermined rotational speed, and moving position determining means for determining a moving position of at least one of the workpiece and the tool every predetermined rotational angle with respect to the predetermined axis, wherein upon a rotational speed change in which the rotational speed about the predetermined axis is changed, at least one of the workpiece and the tool is moved on the basis of the moving position determined by the moving position determining means.
The machine tool driving control apparatus according to the present invention comprises the workpiece rotational speed changing means and moving position determining means, and moves at least one of the workpiece and tool on the basis of a moving position determined by the moving position determining means. In the machine tool driving control apparatus according to the present invention, the moving position of at least one of the workpiece and tool is determined in correspondence with a predetermined rotational angle of a predetermined axis. Even while the workpiece rotational speed changing means modifies the rotational speed of the workpiece about the predetermined axis to a predetermined one, and the rotational speed of the workpiece about the predetermined axis changes, the workpiece can be machined without decreasing the machining accuracy of the workpiece by the tool. Consequently, the workpiece can be machined by the tool even within a time during which machining must stand by in the prior art. machining can be rapidly, efficiently done to increase the productivity.
The machine tool driving control apparatus according to the present invention may be characterized in that the apparatus further comprises reference timing signal generating means for generating a reference timing signal every predetermined rotational angle with respect to the predetermined axis, reference timing signal counting means for counting the number of times of generation of reference timing signals, position data memory means for storing position data which are respectively set in correspondence with count values of a plurality of different numbers of times of generation, and representing moving positions of at least one of the workpiece and the tool, and rotational speed data memory means for storing rotational speed data which are respectively set in correspondence with the count values of the plurality of different numbers of times of generation, and representing rotational speeds of the workpiece about the predetermined axis, wherein, every time the number of times of generation of reference timing signals counted by the reference timing signal counting means reaches a given count value, the moving position determining means reads out position data corresponding to the reached count value and a next count value from the position data memory means, divides a difference between the reached count value and the next count value at predetermined timings, and determines moving positions of at least one of the workpiece and the tool at the divided timings on the basis of the readout position data, and every time the number of times of generation of reference timing signals counted by the reference timing signal counting means reaches a given count value, the workpiece rotational speed changing means reads out rotational speed data corresponding to the reached count value from the rotational speed data memory means, and changes the rotational speed of the workpiece about the predetermined axis on the basis of the readout rotational speed data.
Every time the number of times of generation of reference timing signals counted by the reference timing signal counting means reaches a given count value, the moving position determining means reads out position data corresponding to the reached count value and the next count value from the position data memory means. The moving position determining means divides the difference between the reached count value and the next count value at predetermined timings, and determines moving positions of at least one of the workpiece and the tool at the divided timings on the basis of the readout position data. The reached and next count values are respectively set as start and end points, and a machining shape corresponding to the interval between the start and end points is approximated as a linear section. For this reason, the position data memory means suffices to store position data corresponding to the start point (reached count value) and the end point (next count value). The position data memory means need not store all position data related to the machining shape, and the memory capacity for position data in the position data memory means can be greatly reduced.
The rotational speed data memory means suffices to store rotational speed data between the start point (reached count value) and the end point (next count value). The memory capacity for rotational speed data in the rotational speed data memory means can be greatly reduced.
The position data memory means stores position data representing the moving position of at least one of the workpiece and tool. Thus, moving positions of at least one of the workpiece and tool at divided timings can be quickly determined.
Every time the number of times of generation of reference timing signals counted by the reference timing signal counting means reaches a given count value, the workpiece rotational speed changing means reads out rotational speed data corresponding to the reached count value from the rotational speed data memory means, and changes the rotational speed of the workpiece about the predetermined axis on the basis of the readout rotational speed data. The rotational speed of the workpiece about the predetermined axis can be changed with reference to a count value used to determine the moving position of at least one of the workpiece and tool. As a result, the rotational speed of the workpiece about the predetermined axis can be easily changed.
The machine tool driving control apparatus according to the present invention may be characterized in that the count value is defined to set the position data or the rotational speed data set in correspondence with the count value so as to represent a moving position or a rotational speed at a position where a machining shape is changed, including an inflection point, an angular portion, and a curvature change point in the desired shape.
The position at which the machining shape is changed, such as an inflection point, an angular portion, and a curvature change point in the desired shape, is set as a start or end point, so division of a linear portion in the machining shape of the workpiece is suppressed. Hence, the memory capacity for position data in the position data memory means or rotational speed data in the rotational speed data memory means can be more greatly reduced.
The present invention will be fully understood from the following detailed description taken in conjunction with the accompanying drawings, which are merely examples and do not limit the present invention.
The further application range of the present invention will be apparent from the following detailed description. The detailed description and specific cases will represent a preferred embodiment of the present invention, but are merely examples. Various modifications and improvements within the spirit and scope of the present invention will be apparent to those skilled in the art from the following detailed description.